Renewable oils such as triglyceride oils derived from plant or animal sources and pyrolysis oils derived from lignocellulosic biomass sources are known to contain significant amounts of inorganic contaminants such as alkali and alkaline earth metals, as well as chlorides. The presence of inorganic elements in vegetable oils depends on factors such as type of soil, climatic condition, fruit maturity and extraction and pre-treatment procedures. Further, the level of chloride in lignocellulosic biomass is also dependent on the environment where the biomass is grown. Chloride is of particular concern for the hydroprocessing of these oils to produce hydrocarbon fuels due to the possibility of stress corrosion cracking and corrosion associated with the use of high chloride containing pyrolysis oils. The removal of chlorine compounds from renewable oils prior to upgrading to hydrocarbon fuels is highly desirable to mitigate against chloride induced stress corrosion cracking.
The nature of chlorine in renewable oil has a significant impact on approaches for its removal. Chloride contamination in renewable oils occurs as free chloride, complexed chloride, or organically bound chlorine. Inorganic chlorine in the form of chloride anions should be relatively easy to remove by simple hot water washing. Yet, even refined, bleached and deodorized triglyceride oils sold as food grade edible oils have been shown to contain between 1 and 6 ppm of residual chloride anion. In addition to inorganic chlorine in the form of chloride anions, chlorine could be bound covalently to organic molecules in triglyceride and pyrolysis oils. Natural chlorinated fatty acid and other organic molecules are known to be present in oils derived from marine animals and plants.
Conventional algal oil processing has not provided a satisfactorily efficient process for removing chlorine contaminants from algal oil, whether in the form or free chloride, complexed chloride, or organically bound chlorine. Further conventional algal processing has not provide a satisfactorily efficient process for removing metal contaminants from algal oil. For example, typical methods for removing metals from algal oils include the use of bleaching earths or silica absorbents. These materials are expensive, require significant material handling issue and require disposal of a large volume of solid waste.
Accordingly, it is desirable to provide methods for processing algal oils to effectively remove contaminants including metal or chlorine. Further, it is desirable to provide methods for sequentially performing a base wash and an acid wash on an algal oil during processing. Also, it is desirable to remove contaminants from algal oils before being upgraded to diesel or jet fuel. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawing and the foregoing technical field and background.